83056_04 Genova Bio with TrayCell_CP
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• Introduction One of the most common applications of a UV/Visible spectrophotometer is to measure the concentration of nucleic acids. Often there is very little sample available and the researcher may not wish to dilute it further in order give sufficient volume for measurement in a standard quartz cuvette. Ultra-micro quartz cuvettes are available which will allow as little as 20pl of sample to be measured directly, however they can be quite difficult to use to achieve reproducible results and if the sample needs to be recovered, there may be issues of contamination. An alternative approach, if the sample is of a sufficient concentration, is to use a TrayCell. The TrayCell (Figure 1) is a fibre-optic, ultra-micro cell designed for measurements of extremely small sample volumes of DNA, RNA or protein. The dimensions of the TrayCell are equivalent to a standard 10mm path length cuvette and so will fit in all Jenway spectrophotometers; it is also extremely easy to use. The TrayCell is first positioned in the cell holder of the spectrophotometer and a droplet of sample is placed on an optical window on top the surface of the cell. A cap containing a mirror is then fitted over the top. The type of cap used determines the path length through which the light passes. Light from the spectrophotometer lamp is directed to the sample in the cap by optical fibres; the light returned by the sample is reflected off the mirror in the cap and passed down a second optical fibre to the detector. Figure 1: Schematic diagram of the light path in the TrayCell. Once the measurement has been made, the cap is removed and the sample can be recovered if required. The window and cap are then gently cleaned using a lint-free swab or wipe. The TrayCell remains in the cell holder during all stages; this ensures that the aperture remains in an identical position for each measurement for increased reproducibility. • Virtual dilution Two caps (1mm and 0.2mm) are supplied with the TrayCell which create defined optical light paths of 1mm and 0.2mm respectively. Caps giving 2mm or 0.1mm path length are also available as accessories. The reduced path length (compared to a standard 10mm cuvette) generates a virtual dilution of the sample with a dilution factor of 1:10 for a 1mm cap or 1:50 for a 0.2mm cap. This allows the user to measure the sample and recover it cptechsupport@coleparmer.com | Tel: +44 (0)1785 810433 | 08/2017

Table 1: Measured DNA concentrations of each sample dilution using the TrayCell and micro volume cuvette. Shaded cells show results where A260 was <0.025.

The results demonstrate that the TrayCell gives comparable values to the samples measured in conventional 10mm path length cuvettes up to the limit of the spectrophotometer absorbance range. The results also clearly show that due to the virtual dilution factor of the TrayCell caps, it is possible to measure DNA of a much higher concentration (greater than 125^g/ml) than standard cuvettes avoiding dilution of the sample. Limitations for the TrayCell occur at lower concentrations. Based on the standard estimation of dsDNA that a 50^g/ml solution gives absorbance of 1.0 at 260nm and also that...

• Conclusions The TrayCell is a useful tool for measuring the absorbance of samples where there is limited sample available or the sample needs to be recovered after measurement without dilution. The required sample volume for the 1mm cap is 3^l to 5^l and for the 0.2mm cap, 0.7^l to 4^l. Therefore if the sample is sufficiently concentrated, only a very small volume is required. Concentration values obtained with the TrayCell are comparable to those obtained with standard 10mm path length cuvettes. Further advantages include quick and easy cleaning and strictly defined path lengths meaning...